Composition for smelting hearths



Patented 27,

PATENT OFFICE! CYRANO TAIL, OF BEBLm-SCHONEIBEBG,

'THERMIC CORPORATION, OF AJAX PARK, NEW

JERSEY GERMANY, assrcnoarqmax mncrao JERSEY, A CORPORATION OF NEWcourosrrron r03; smnr'rme nmnrns' No Drawing. Application filed January16, 1981, Serial No. 509,278, and in Germany January 17, 1980.

My invention relates to linings for electric induction furnaces.

A purpose of my invention is to employ a lining in an electric inductionfurnace containing, beryllium oxide, and preferably also a material toassist in fritting.

For the manufacture of smelting hearths of induction furnaces,especially of crucibleshaped high-frequency furnaces,. without channels,generally known as coreless such refractory materials as magnesite,electrically fused magnesia, corundum,

chrome ore, oxide of zirconium, quartz sand, mullite,

spmel,

' and the like, have been used. All these materials are suited, it istrue, to the manufacture of the refractory linings mentioned, but someof their properties are disadvantageous Too great a heat-conductivity,for instance, with corundum, as well as with electrically fusedmagnesia, causes great losses of heat through the crucible walls. Incontradistinotion to the other known furnace constructions, in which agreat heat conductivity of the crucible material is desired, therefractory lining of an induction .fiirnac'e requires preferably arefractory mapy terial having a low heat conductivity, as the energy isnot introduced by, conduction through the refractory lining, but isdeveloped directly within the charge. Besides, too high an electricalconductivity of'the refractory linings is detrimental, as it issometimes necessary to operate an inductor coil with a high voltage,which when used in connection with 'a refractory material having a highelectrical conductivity is likely to entail detrimental consequence.Other detrimental properties of the linings of the prior art are theirlow compressive strength, seen, for instance in chromium fettlings andlinings, their chemical instability, evident in oxide of zirconium,their low softening points, asis the case with silicious fettlings andlinings, and finally, their large expansions and contractions.

In the present invention I employ for the linings of electric inductionfurnaces, a material distingu shed by its low heat conductivity and forits high softening point (more as is found,

oxide of molybdenum, MoQ

than 2000 C.) and its low coefiicient of expansion.

According to this invention, the smelting hearth contains from to 98% ofberyllium oxide, as this substance possesses all of the above-mentionedproperties; Furthermore,

refractory linings made from beryllium oxide of suitable grain size. andwith suitable content of mineralisators (that is, those substanceshaving a catalytic action in inducing sintering), in accordance with thewell known principles of refractory manufacture, are very resistant tomechanical abrasion due to the circulation which is a peculiar featureof coreless induction furnaces. I I

. Preferably, the beryllium oxide is mixed with other refractory oxides,according to the particular purpose for which it is intended. Formelting metals with a high fusing point, as metals of the platinum andof the chromium group, instance, of beryllium oxide and. a frittin gsubstance vsuch as oxide of tungsten, W0 pyroboric acid ro-phosphoricacid, sesquloxide of bismuth and the like has proved particularly suitedfor the purpose in view.

. I find it highly desirable to make up part of the refractory lining ofone of the well known refractory oxides. I include in this group aconsiderable range of substances heretofore used as refractory liningsin electric induction furnaces. Where I desire, I may mix severalrefractory oxides with the beryllium oxide in a single lining.

Typical examples of refractory oxides are the oxides of magnesium,.chromium, zirconium and thorium. I may also very desirably include withthe beryllium oxide one or -more refractory oxides, and suitablefritting substances.

I claim 1. A-refractory lining for induction furnaces, containing from20 to 98% of beryllium oxide and another refractory material.

2. A refractory lining for induction furnaces, containing from 20 to 98%of beryllium oxide and a refractory oxide.

V 3. A refractory lining for induction fura hearth consisting, for

naces containmg' from 20 to 98% of llilum bxide and a plurality ofrefractor y gx- 1 es.

4. A refractory lining for induction furnaces, containing from 20 to 98%of beryllium oxide and a substance of the group m eluding magnesiumoxide, oxide, zircomum oxide and thorium oxide.

5. A refractory lining for induction fur- 10 naces, containing from 20to 98% of beryllium oxide and a fritting substance.

6. A refractory for induction furnaces, containing from 20 to 98%, ofberylhum oxide and a substance of the group 1n I ll eluding oxide oftungsten, oxide of molybdenlum, 'pyroboric acld and pyrophosphoric' ac17. A refracto limng' for induction fur-' naces, containin g from 20 to98% ofberyl- N lium oxide with an addition of a refractory oxide and afrittin substance. 8. A refractory g for induction furnaces, containingfrom 20 to 98% of beryllium oxide with an addition of a plurality ofrefractory oxides and a fritting substance.

In testimony whereof I aflix my ature. 0mm T I

